System For Milling And Air-Water Cooling Bottom Ash From Heating Furnaces For Solid Fuels

ABSTRACT

The present invention relates to a milling and water-air combined cooling system for bottom ash from heating furnaces for solid fuels, able to maximize the efficiency in milling and cooling also large ash lumps at high temperature and in improving cooling air fluid dynamics which passes said system in counter-flow. The system comprises a crusher ( 1 ) provided with a pre-crusher integral with the crusher&#39;s ( 1 ) port, a water cooling system ( 3 - 4 ), and a separation ( 5 - 6 ) of the flow of the fine material entering the crusher ( 1 ) from the lump sized ash. The pre-milling device ( 2 ) allows a partial milling of the large lumps and it is actuated by laser or equivalent sensors ( 7 ) which detect the presence of ash agglomerates in the milling area. The cooling water passes preferably throughout the shaft ( 8 ) of the toothed rotor ( 9 ) and/or throughout the fixed slab ( 10 ) and moves therefrom, through suitable ducts ( 4 ) and nozzles ( 3 ), to the milling area. The water intervention is automated depending on the crusher rotor&#39;s ( 9 ) or casing&#39;s ( 11 ) temperature detected by suitable sensors ( 12 ). The flow separation of the fine material is achieved creating an opening ( 13 ) at the rear wall of the crusher and isolating it by a counterweight or automatic valve ( 5 ) at the unloading channel ( 14 ) and a closing shield ( 6 ) downstream of the traction head of the fine ash recuperator ( 15 ).

In the dry ash extraction systems (see EP 0 471 055), cooling ash on the offload conveyor and the subsequent conveyors is achieved by forced-convection heat exchange with air returning to the system once it has been pulled out by depression value occurring at the bottom of the furnace. Cooling air is introduced throughout suitable ports located at the sidewalls of the extractor and the subsequent conveyors and it runs over the ash while passing through the line of counter-flow conveyor machines until it reaches the combustion chamber. The system provides one or more milling stages between the extractor and the subsequent conveyor/cooler, as well as between two subsequent conveyors, in order to increase efficiency in air-ash heat exchanging. Such milling systems by reducing particle size of the ash increase available surface thereof for heat exchange with the counter-flow air. In the conventional extraction system either the main extractor receiving ash from furnace either the subsequent conveyors are provided with fine ash recuperators located at the bottom. The recuperated ash is then unloaded together with heavy ash lumps on the next machine.

Along the cooling air path backwardly relative to machine line till it reaches the combustion chamber, passing from a machine to the previous one is particularly critical in the presence of the crusher. Going up again to the crusher and then to the loading hopper the air drags portion of fine material recuperated by leading it back to the bottom zone where the fine ash recuperator is installed and by causing accumulation in the machine bend. Those time-repeated trends generate difficulties about wear much more important than those expected during normal operation, malfunctions and also locking of the fine ash recuperating system which operates anomalously with a flow rate value higher than the in-design one. In order to avoid that condition the known system provides a by-pass duct with a suitable diameter connecting extractor top cover, in vicinity of unloading point, to the subsequent conveyor cover, in a position just downstream in respect of the unloading point. The aim is to allow a preferential path for the cooling air, while passing from a conveyor to the previous one, by starting it from the top of the ash conveyor belt. However this solution reduces the ash cooling efficiency a lot, because only a minimum amount of air crosses the crusher where the heat-exchange efficiency is maximum due to opening of the ash flow falling in the crusher and to reduction of lump size achieved by crushing members that cause the available forced-convection heat-exchange surface of the ash to increase.

Further, large agglomerates of bottom ash, coming from the furnace, are cooled by air only outside so that inside themselves they can maintain a doughy state, in this case the crusher milling function decreases greatly being able to generate only some grooves on the ash agglomerate which is not milled by the action of the toothed roller. This condition causes accumulation problems for the crusher, with needs of intervention in order to clear the port and allow normal material flow and generates an unavoidable increasing in working temperature of the milling members and crusher casing, a strong decrease of wear strength occurring as well as a fast consumption of the milling members.

All of these problems are solved by the milling and cooling system according to the present invention, able to maximize milling and bottom ash cooling efficiency also in presence of large high-temperature agglomerates and improve fluid dynamics of the cooling air with consequent elimination of malfunctions ad excessive wear for fine material recuperating machines.

Thanks to suitable expedients like the normally closed automatic valve in the by-pass duct and the separation of the fine ash unloading from lump sized ash, the fluid dynamics of the cooling air and the air/ash heat-exchange efficiency improve highly in respect of the conventional system. All of the air flow, indeed, is passed throughout the crusher where the air/ash cooling efficiency is maximum due to the ash free fall in forced air and the wider surface available for heat exchange thank to the crushing action. The separation of the fine ash unloading is achieved forming a dedicated opening at the rear wall of the crusher, to which an unloading channel of the ash recuperating machine is connected and by isolating said unloading from crusher environment by means of a valve located in the unloading channel and a closing shield downstream of the traction head of the fine ash recuperator. The position of the fine ash entry to the crusher is such as to avoid pass through the milling zone for the fine ash and showing itself as a compact flow and any more dispersed in free fall, it results hardly entrainable by the cooling air crossing in counter-flow the crusher.

Efficiency in milling and cooling large ash lumps at high temperature is maximized due to presence of a pre-crusher and the water cooling system.

The pre-crusher function is to execute a first milling of large ash lumps at high temperature that obstruct the crusher port, making the rotor teeth milling action faster and more efficient. The pre-crusher intervention is activated by a laser or equivalent sensor which senses the presence of incoming large ash lumps within milling area.

Water for the cooling system is supplied preferably through the rotor axis and/or at the base of fixed slab and passes therefrom in the milling area through nozzles placed in the toothed rotor and/or in the fixed slab. Said cooling system is actuated by increase of the temperature values of the toothed roller and the crusher casing, detected by means of suitable sensors, and determined by presence of ash, or large agglomerates, at high temperature. The water flow rate to be supplied to the nozzles can be adjusted depending on temperature of the ash leaving the crusher and detected on the downstream machine by a suitable sensor. Steam occurring during cooling process, thanks to the separation of the crusher environment from the fine ash recuperator, will be dragged by the cooling air directly to the combustion chamber.

This system configuration allows numerous and notable advantages since it removes obstructions and early wear for the fine ash recuperator, reducing wear of the crusher which has any more to process fine material too, the efficiency of the heat exchange between air and ash is taken to the maximum since all the cooling air collides with the ash during falls between one conveyor machine and the next one and the cooling and milling process is optimised also for large ash lumps at high temperature further achieving an effective cooling of the crusher.

The innovative features, the objects and the advantages of the present invention will become apparent from the following description and the appended drawings of the not limiting embodiments in which the different figures show:

FIG. 1 shows a cross-sectional view of the integrated milling and air/water cooling system.

FIG. 2 shows a schematisation of positioning of the integrated milling and cooling system inside of the extraction and cooling air flow system throughout the system.

FIG. 3 shows a milling and air/water cooling system axonometric projection.

In this connection it is desirable to point out that like reference numbers in the different figures indicate the same or equivalent parts.

The milling and cooling system hereinafter described permits numerous and notable advantages because: it improves cooling air fluid dynamics with consequent removal of malfunctions and excessive wear for fine ash recuperating machines and crusher wear reduction, the efficiency of the heat exchange between air and ash is taken to the maximum since all the cooling air collides with the ash during falls between one conveyor machine and the next one and the cooling and milling process is optimised also for large ash lumps at high temperature further achieving a effective cooling of the crusher milling members.

The system is constituted by a crusher 1 provided with a single, or dual, toothed roller 9, a pre-milling device 2, air 3 and water 4 cooling system and characterized by a side inlet 13 for fine material separate from lump sized ash inlet.

The separate fine ash unloading 5, 6, 13 from the crusher 1 is formed by a suitable channel 14, independent from main ash unloading 16, connected to a suitable opening 13 formed in the rear wall of the crusher 1. The fine ash inlet position to the crusher 1 is such as to avoid it crossing the milling members 9. Inside the fine ash unloading channel 14 a counter-weight or automatic valve 5 allows discharge of fine material preventing air intake within the recuperator when it crosses the crusher counter-flow. Moreover a closing shield 6 placed downstream of the traction head 15 of the fine ash recuperator allows to isolate this zone from the conveyor machine unloading zone 16 and to remove air recurrences within the fine ash recuperator 15. By means of these expedients and the use of a normally closed automatic valve 17 placed at the by-pass duct passing the cooling air throughout the crusher 1 is allowed taking the air/ash heat exchange to the maximum and also avoiding excessive wear problems and recuperating system's 15 malfunctions. The automatic valve 17 at the by-pass duct permits passing of the cooling air only in case of obstruction of the crusher 1 detected by a differential pressure transmitter which detects a pressure increase downstream of the crusher 1.

During passing of the air throughout the crusher 1 air/ash heat exchange is maximum since free fall is used and so the opening of the ash flow in forced air and a wider surface available for heat exchange after milling the ash.

The water cooling system 3-4 allows an additional cooling for large ash agglomerates at high temperature and it is operated depending on the rotor's 9 and casing's 11 temperature, detected by suitable sensors 12, which increases due to the presence of large lumps and/or ash high flow rate at high temperature in the milling area.

The water cooling system 3-4 provides sprinkling nozzles 3 arranged preferably within the rotor 9 and/or the fixed slab 10. The water supplied through the shaft 8 of the rotor 9 and/or above the fixed slab 10, reaches the milling area through suitable ducts 4 and nozzles 3 cooling the ash entering the crusher 1 and simultaneously helping in cooling effectively the working members 9-10. The water flow rate adjustment for the nozzles 3 is obtained depending on the temperature of the ash exiting the crusher 1 detected by a suitable sensor 19 on the machine downstream the crusher.

The steam occurring during the cooling process, thanks to the separation 5-6-13 of the crusher's 1 environment from the fine ash recuperator 15, will be dragged by the cooling air directly into the combustion chamber avoiding problems for the recuperating machines 15.

The pre-crusher 2 is constituted by plates with punches 20 made by suitable anti-wear material, that slide opposing on a fixed frame 21 connected to the crusher's 1 port, and actuated by hydraulic cylinders 22. Such a device facilitates and speeds up actions of the rotor's 9 teeth of the crusher 1 when ash large lumps at high temperature obstruct inlet thereof, by moving and partially milling them by movement of the plates with punches 20. The pre-crusher's 2 intervention is controlled by a laser or equivalent sensor 7 which detects presence of ash large lumps in the milling area.

The air and water cooling and milling system according to the present invention, besides the huge functional advantage in improving cooling air fluid dynamics with consequent removal of obstructions and stoppages of the crusher 1 and the fine ash recuperators 15, provides a more comfortable and faster milling also of large ash agglomerates at high temperature, helping, by an indirect cooling of the milling members 9, in increasing the expected life of the crusher 1. 

1. A milling and air and water cooling system for bottom ash from heating furnaces for solid fuels, able to maximize efficiency in: milling and cooling also large ash lumps at high temperature and improving cooling air fluid dynamics using the integrated action of a pre-crusher (2) integral with the crusher's (1) port, a water cooling system 3-4 and the separation of the fine material flow, entering the crusher (1), from the lump sized ash, that permits the most suitable passing of the crusher (1) for the cooling air counter-flow relative to the ash flow, avoiding entrainment of the recuperated fine material.
 2. The milling and air and water cooling system according to claim 1 characterized by the presence of a pre-crusher (2) integral with the crusher's (1) port formed by slabs with punches (20), made of suitable anti-wear material, which slide opposing on a fixed frame (21) connected to the port of the crusher (1), and actuated by hydraulic cylinders (22), functioning as pre-crusher of large ash lumps obstructing the crusher's (1) inlet thanks to the action of the slabs with punches (20).
 3. The milling and air and water cooling system according to claim 1 characterized by the fact that water of the cooling system passes preferably throughout the shaft (8) of the toothed rotor (9) and/or though the fixed slab (10) and moves therefrom, through suitable ducts (4) and nozzles (3), in the milling area cooling the ash entering the crusher (1) and indirectly the milling members (9).
 4. The milling and air and water cooling system according to claim 1 characterized by the separation of the fine material inlet within the crusher (1) from the lump sized ash achieved by a dedicated opening (13) at the rear wall of the crusher (1), which is connected to the unloading channel (14) and a closing plate (6) downstream of the traction head of the fine ash recuperator (15); all of this allowing the counter-flow passing of the crusher for the cooling air avoiding entrainment of recuperated fine ash.
 5. The milling and air and water cooling system according to claim 2 characterized by the fact that the pre-crusher's (2) intervention is controlled by a laser or equivalent sensor (7) which detects presence of large ash lumps in the milling area.
 6. The milling and air and water cooling system according to claim 3 characterized by the fact that the water cooling intervention is controlled by the rotor's (9) and casing's (11) temperature value detected by suitable sensors (12) whilst the water flow rate adjustment to the nozzles (3) is carried out depending on the temperature of the ash exiting the crusher (1) detected by a suitable sensor (19) on the machine downstream the crusher (1).
 7. A system for crushing relatively large ash lumps or cinders from a solid fuel furnace which comprises a fine ash separator (15) for separating fine ash from the lumps or cinders; a precrusher (2) adapted to receive from the separator (15) separated lumps or cinders; a crusher (1) having an inlet in communication with the precrusher (2) and adapted to receive lumps or cinders processed in the precrusher (2); a crusher by-pass unloading conduit (14) for preventing separated ash from entering the crusher (1); a water supply (3, 4) for introducing cooling water into the crusher (1); and means for introducing a counter current air flow through the crusher (1) and precrusher (2). 